Feature placement doesn't check for biomes, causing unnecessary lag

Hi- here's the code that I found to solve the performance issue without causing feature placement regressions at biome borders, in ChunkGenerator#

applyBiomeDecoration:

Set<Biome> seenBiomes = new HashSet<>();
for (int x1 = -1; x1 <= 1; x1++) {
    for (int z1 = -1; z1 <= 1; z1++) {
        ChunkAccess chunk = worldGenLevel.getChunk(chunkX + x1, chunkZ + z1);

        for (LevelChunkSection section : chunk.getSections()) {
            for (int ax = 0; ax < 4; ax++) {
                for (int ay = 0; ay < 4; ay++) {
                    for (int az = 0; az < 4; az++) {
                        seenBiomes.add(section.getBiomes().get(ax, ay, az));
                    }
                }
            }
        }
    }
}

List<List<Supplier<ConfiguredFeature<?, ?>>>> features = new ArrayList<>();
for (Biome biome : seenBiomes) {
    List<List<Supplier<ConfiguredFeature<?, ?>>>> featuresInBiome = biome.getGenerationSettings().features();

    features.addAll(featuresInBiome);
}

The other change that would be needed is to change the iterator's next() to be next().get(). It would be possible to flatten the suppliers, but I figured that there was no harm in keeping it like this. This would replacing getting all the configured features via the biome source.

The reasoning behind this change is that features can't expand beyond a 3x3 of chunks centered on the current chunk, so it would be possible to optimize by making it so features that would never have a chance of placing anyway would not be considered for spawning.

This code is CC0 and can be used freely.

Can confirm

I also noticed this problem a while ago when researching MC 1.13 code. All features attempt to generate in all chunks, the most funny being Nether Fortress trying to generate in the Overworld. Trying to find the screenshot I had of the code running, but that might take a while.

Can confirm in 21w44a.
Vanilla control: 60 seconds
Lag control: 149 seconds

The data pack no longer works in 1.18 Pre-release 1, but this is probably still an issue.

Extreme lag between oceans and land biomes I discovered.